This invention relates to real time suspension controls for motor vehicles, and particularly to such controls responsive to a vertical vehicle body absolute velocity parameters derived by integration from a vertical absolute acceleration sensor mounted on the vehicle body.
A key parameter for use in the control of some vehicle suspensions is the absolute vertical velocity at some point of the vehicle body. At present, there exist no practical absolute velocity sensors for directly measuring this parameter. It can be obtained, however, by integrating the output of a vertical absolute acceleration sensor at the same point, provided that the acceleration sensor output signal is high-pass filtered to remove all DC components that might otherwise cause integrator saturation and drift.
The natural frequency of vibration of a typical vehicle body is in the range 1-2 Hz. To prevent loss of information in this frequency range, a high pass filter must have a steep rise from zero Hz (DC), where full suppression is desired, to the beginning of its passband at 1 Hz, where minimum suppression is desired. Using a traditional, one pole filter design and an integrator with a low frequency, one pole rolloff for additional high pass filtering, the filter pole resides very close to the integrator pole; and quantization error becomes significant in a digital machine embodiment of the filter. A sixteen bit, fixed point, digital processing (DSP) machine is desirable for its comparatively low cost; but substantial integrator drift may occur with a standard one pole high pass filter on such a machine due to quantization errors. Alternative fixed point DSP machines with greater resolution or floating point computing machines increase the cost.